HONG KONG -- Formaldehyde, which has been linked to cancer, has legitimate uses in adhesives and embalming. But in Indonesia, Sutikno, a 35-year-old tofu maker in south Jakarta who goes by one name, uses it to keep the tofu he sells fresh.

"Formaldehyde is magic. There is no comparison," he said on a recent afternoon at the market. Last year, he switched briefly to a legal preservative, but his bean curd went bad in less than 24 hours. As for his customers, he doesn't tell them he uses formaldehyde. "There is no complaint," Mr. Sutikno said.

Across Asia, small-scale food manufacturers and street vendors often boost profits by using cheap but toxic chemicals as sweeteners, dyes and preservatives. While the most egregious examples generally involve food for local consumption, dangerous additives occasionally end up in foods exported to the U.S. and other Western countries, highlighting the scope of the problems regulators face.

"Human ignorance as well as greed knows no bounds," says Gerald Moy, manager of the World Health Organization's office that monitors chemicals in the global food supply.

The pet-food contamination that killed and sickened cats and dogs in the U.S. has called into question the safety of imports from China. Yesterday China's General Administration of Quality Supervision, Inspection and Quarantine said on its Web site that Xuzhou Anying Biologic Technology Development Co. and Binzhou Futian Biology Technology Co. exported the toxic ingredients which contained melamine, a chemical used in fire retardants. The companies weren't available to comment this morning.

Separately, U.S. Food and Drug Administration officials yesterday said they found melamine in Canadian-manufactured fish meal containing what was labeled as wheat gluten imported from China. The officials said they are looking at fish meal imported not only from China but also from other countries. Melamine-contaminated ingredients found in pet foods were actually wheat flour, rather than wheat gluten or rice protein concentrate as labels indicated, the officials added.

The FDA has the authority to inspect food shipments, but because of the sheer volume of imports, only a fraction of food entering the country is inspected. "Our focus is based on where we know the risks are," David Acheson, the FDA's assistant commissioner for food protection, said in an interview. "It's not a strategy to test everything that arrives at the ports." But the FDA says it is rethinking its strategic approach to targeting potential risks and allocating resources. It is also working with the Chinese watchdog group to search for long-term solutions, Mr. Acheson said.

With the discovery of melamine in animal food, the agency is considering a new safety system for animal feed that would go beyond the current focus on preventing mad-cow disease and salmonella.

In Asia, unsafe additives in foods for human consumption have long been a problem. Some street vendors use an industrial dye for textiles called Sudan Red to make their coconut and sugar-cane drinks look more attractive. "You could just see the beverages, they sort of glow, because these dyes are really quite intense," says the WHO's Mr. Moy. Last November, Chinese authorities discovered that poultry farmers in Hebei province had been using one of the Sudan Red dyes, believed to cause cancer, to color the feed of their ducks and redden the yolks of the eggs, which sell at a premium price.

In 2003, Sudan Red was found in hot-chili products imported from India to the U.K. Products containing the dye were also recalled in Canada and South Africa. Over the next two years, the contamination snowballed. By March 2005, 580 products had been withdrawn in the U.K.

In March this year, the FDA stopped 215 shipments from mainland China for a variety of problems. One shipment of dried dates was considered filthy; plums contained unsafe sweeteners; and oranges had pesticide residues. A few dozen also had unsafe color additives. But there is often a disconnect between what regulators charge and companies respond. One of the shipments the FDA refused was apple chips from Hebei Dongfang Green Tree Food Co. in China, which may have contained unsafe color additives.

Pan Yanjun, the company's vice president, confirmed in a telephone interview yesterday that his company shipped some apple chips to the U.S. in March for a natural food show, but said that the FDA approved the shipment. "We never dye the apple chips," he said.

There is little evidence that foods contaminated by unsafe preservatives are being shipped abroad. But unauthorized use is widespread in Asia.

Formaldehyde, for instance, is often used as a preservative in Asia and other parts of the world where refrigeration is scarce. In late 2005, the Indonesian National Agency for Drug and Food Control tested 161 samples of fish, shrimp, squid, tofu, and noodles produced and sold across six cities and found that 64 of the samples tested positive for formaldehyde.

Another problem is a group of chemicals called borates, including boric acid. Borates were widely used in food products in the U.S. and other countries a century ago to improve the texture of food as well as preserve it. Most countries today prohibit its use as a food additive because it is toxic at high levels. Now, the chemical is mainly used in insecticides, flame retardants and cleaning products.

In March and April of 2006, the Malaysian Health Ministry tested 387 samples of rice noodles, 20 of which were found to contain boric acid, according to Dr. Abdul Rahim Mohamad, the director of the food safety and quality division within Malaysia's Health Ministry.

In Thailand, Peerapong Suksaweng, an official with the country's Food and Drug Administration, runs spot checks on street vendors, supermarkets and farmers' markets. Each day, his mobile inspection unit -- one of 26 throughout the country -- checks produce for insecticides and chemical additives such as borates and formaldehyde.

He has found street vendors who have added borates to minced pork and meatballs to keep them fresh. In high quantities, Mr. Peerapong says, "people who eat [that] could vomit blood or die."